Numerical simulations of the frictional collisions of solid balls on a rough surface   总被引：1，自引：0，他引：1  

S. Mathavan  M. R. Jackson  R. M. Parkin 《Sports Engineering》2014,17(4):227-237

Three-dimensional simulations of the frictional collision between solid balls moving on a rough surface are analyzed in this paper. The analysis is performed in the context of pool and snooker, two popular games in the pocket billiards family. Accurate simulations of ball motion in billiard games are useful for television broadcasts, training systems and any robotic game playing systems. Studying solid ball collisions in a three-dimensional space requires careful consideration of the different phenomena involved in ball motion such as rolling, sliding and ball spin about a general axis. A set of differential equations are derived describing ball dynamics during collisions. In the absence of explicit analytical solutions to the differential equations, a numerical procedure is performed to determine post-collision ball velocities and spins after collision. In addition, the paper also presents a methodology to analyze the curved, slip trajectories of balls immediately after impact. The results presented here, when compared with some experimental shots, show that the percentile errors in post-collision velocities are reduced by the proposed method. The prediction accuracies for ball travel direction are increased twofold by the proposed impact simulation algorithm.  相似文献   

A novel miniature dynamic microfluidic cell culture platform using electro-osmosis diode pumping     

Jen-Yung Chang  Shuo Wang  Jeffrey S. Allen  Seong Hyuk Lee  Suk Tai Chang  Young-Ki Choi  Craig Friedrich  Chang Kyoung Choi 《Biomicrofluidics》2014,8(4)

An electro-osmosis (EOS) diode pumping platform capable of culturing cells in fluidic cellular micro-environments particularly at low volume flow rates has been developed. Diode pumps have been shown to be a viable alternative to mechanically driven pumps. Typically electrokinetic micro-pumps were limited to low-concentration solutions (≤10 mM). In our approach, surface mount diodes were embedded along the sidewalls of a microchannel to rectify externally applied alternating current into pulsed direct current power across the diodes in order to generate EOS flows. This approach has for the first time generated flows at ultra-low flow rates (from 2.0 nl/s to 12.3 nl/s) in aqueous solutions with concentrations greater than 100 mM. The range of flow was generated by changing the electric field strength applied to the diodes from 0.5 Vpp/cm to 10 Vpp/cm. Embedding an additional diode on the upper surface of the enclosed microchannel increased flow rates further. We characterized the diode pump-driven fluidics in terms of intensities and frequencies of electric inputs, pH values of solutions, and solution types. As part of this study, we found that the growth of A549 human lung cancer cells was positively affected in the microfluidic diode pumping system. Though the chemical reaction compromised the fluidic control overtime, the system could be maintained fully functional over a long time if the solution was changed every hour. In conclusion, the advantage of miniature size and ability to accurately control fluids at ultra-low volume flow rates can make this diode pumping system attractive to lab-on-a-chip applications and biomedical engineering in vitro studies.  相似文献   

Challenges in the evaluation for possible abuse: presentations of congenital bleeding disorders in childhood     

Jackson J  Carpenter S  Anderst J 《Child abuse & neglect》2012,36(2):127-134

  相似文献   

Envisioning a New Agriculture     

Wes Jackson 《Public Library Quarterly》2013,32(1):76-79

In this letter, the director of the Institute, Wes Jackson, contrasts the agriculture he sees in a nearby cultivated field versus the agriculture that Americans need to sustain farm land and the human food supply. Jackson suggests that “a new agriculture” is the only way we will improve the quality of our land and increase the reliability of our food supply.  相似文献   

Decentering the teacher: a practitioner's acccount     

Allen Trent 《Teachers and Teaching》2013,19(4):295-307

This article is an account of an action research project conducted in a first grade classroom. The practitioner-researcher describes a process of “decentering.” Realizing that centering learners necessarily means decentering the practitioner, the author collaborates with his first grade class to identify and clarify the problems associated with teacher centeredness. This article describes the groups' development and implementation of strategies and includes reflections upon understandings and project-derived assertions. The account presents students' perspectives and interpretations and the practitioner's emergent theories as they evolved throughout this collaborative endeavor. The author asserts that the research has potential relevancy to a variety of other teaching contexts.  相似文献   

Integrating theory and practice in the pre-service teacher education practicum     

Jeanne Maree Allen  Suzie Elizabeth Wright 《Teachers and Teaching》2013,19(2):136-151

This article reports on a study into student teachers’ perceptions about their professional development during practicum. Framed within a symbolic interactionist perspective, the study examined to what extent, and how effectively, one group of student teachers was able to integrate theory and practice during a three-week practicum in the first year of their degree. The context for this mixed methods study was a Master of Teaching, graduate-level entry programme in the Faculty of Education at an urban Australian university. Although there is a strong field of literature around the practicum in pre-service teacher education, there has been a limited focus on how student teachers themselves perceive their development during this learning period. Further, despite widespread and longstanding acknowledgement of the ‘gap’ between theory and practice in teacher education, there is still more to learn about how well the practicum enables an integration of these two dimensions of teacher preparation. In presenting three major findings of the study, this paper goes some way in addressing these shortcomings in the literature. First, participants in this study largely valued both the theoretical and practical components of their programme, which stands in contrast to the commonly identified tendency of the student teacher to privilege practice over theory. Second, opportunities to integrate theory and practice were varied, with many participants reporting the detrimental impact of an apparent lack of clarity around stakeholders’ roles and responsibilities. Third, participants overwhelmingly supported the notion of linking university coursework assessment to the practicum as a means of bridging the gap between, on the one hand, the university and the school and, on the other hand, theory and practice.  相似文献   

Perspective     

David Allen 《Perspectives: Policy and Practice in Higher Education》2013,17(2):32-34

  相似文献   

Setting up school partnerships: some insights from Birmingham's Collegiate Academies     

Dr Desmond Rutherford  Lindsay Jackson 《School Leadership & Management》2013,33(5):437-451

This article explores the key issues or dilemmas secondary schools face when considering collaborating to form a school partnership, in particular a Collegiate Academy. The methodology is an evaluation based on interviews with 15 headteachers and other key staff from three Collegiate Academies in Birmingham during the autumn of 2005. Seven key issues are identified – size, coordination, focus, needs, success, funding and dissemination – that schools need to work through and resolve if their partnership is to be successful. An analysis of the interconnections among the seven issues shows three underlying themes: the first relates to the organisation of the Collegiate Academies; the second concerns the work of the collegiate-based Advanced Skills Teachers; and the third encompasses sustainability and securing the long-term future of the Collegiate Academies. School partnerships are increasingly seen by government as the key to school improvement and so the findings from this preliminary study have potential benefits, particularly in the initial phase of setting up such partnerships.  相似文献   

Whole school support for vulnerable children: the evaluation of a part‐time nurture group     

Lynne M. Binnie  Kristen Allen 《Emotional and Behavioural Difficulties》2013,18(3):201-216

The positive impact that nurture groups can offer is well documented. This study aims to describe the evaluation of a nurture group intervention across six schools. In contrast to previous research, children accessed the group for a maximum of four mornings per week. The findings show that this model did not comprise the gains reported in previous studies. The results show a significant positive effect on the children with reference to their behaviour both in school and at home. In addition, the intervention appears to have contributed further to the whole school system. Schools reported an improved ethos and an increased capacity to support children with social and emotional difficulties. This paper concludes by considering the new Scottish Curriculum guidelines A curriculum for excellence and whether the principles and theoretical underpinnings of nurture groups can be fully integrated into a mainstream environment.  相似文献   

A latent transition analysis of academic intrinsic motivation from childhood through adolescence     

George A. Marcoulides  Adele Eskeles Gottfried  Allen W. Gottfried  Pamella H. Oliver 《Educational Research and Evaluation》2013,19(5):411-427

A longitudinal modeling approach was utilized to determine the existence of latent classes with regard to academic intrinsic motivation and the points of stability and transition of individuals between and within classes. A special type of latent Markov Chain model using Mplus was fit to data from the Fullerton Longitudinal Study, with academic intrinsic motivation measured from ages 9 through 17. Model fit using the Bayesian Information Criterion index was examined. The best fit involved a 3-class model, with classes designated as motivationally gifted, intermediate, and at-risk. Transitions between classes occurred mainly during childhood, whereas stability ensued by age 13. Methodological contributions are discussed, as well as theory and applications of the findings with regard to academic intrinsic motivation.  相似文献